refactor: move impls to arch/ directory #295

Job	Run time
docs	29s
Clippy	26s
feature checks	1m 29s
fmt	15s
Fuzz	56s
Miri (x86_64-unknown-linux-gnu, --no-default-features)	1m 4s
Outdated	5s
Miri (x86_64-unknown-linux-gnu)	1m 13s
Miri (x86_64-unknown-linux-gnu, --all-features)	1m 31s
Test (x86_64-unknown-linux-gnu, nightly)	27s
Miri (x86_64-unknown-linux-gnu, --features force-generic)	1m 16s
Test (x86_64-unknown-linux-gnu, beta)	24s
Miri (aarch64-unknown-linux-gnu, --no-default-features)	1m 10s
Test (x86_64-unknown-linux-gnu, stable)	22s
Miri (aarch64-unknown-linux-gnu)	1m 15s
Test (x86_64-unknown-linux-gnu, 1.64)	33s
Miri (aarch64-unknown-linux-gnu, --all-features)	1m 38s
Test (aarch64-unknown-linux-gnu, nightly)	58s
Miri (aarch64-unknown-linux-gnu, --features force-generic)	1m 13s
Test (aarch64-unknown-linux-gnu, beta)	1m 0s
Test (aarch64-unknown-linux-gnu, stable)	42s
Test (aarch64-unknown-linux-gnu, 1.64)	54s
	19m 20s

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